Flexible construction of three-dimensional continuous conductive structure by hollow carbon sphere and CNT for promoted ions transport in flow-electrode capacitive deionization

• Published in: Separation and purification technology Vol. 337; p. 126405
• Main Authors: Cai, Yanmeng, Zhao, Fei, Zhao, Jinsheng, Wang, Yue
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 13.06.2024
• Subjects: Bridging effect; Effective collision; Flow-electrode capacitive deionization; Interfacial charge transfer; Rheological behavior; Bridging effect; Flow-electrode capacitive deionization; Rheological behavior; Effective collision; Interfacial charge transfer
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2024.126405

[Display omitted] •The 3D continuous conductive network HCS@CNT is flexibly constructed as flow-electrode.•HCS@CNT flow-electrode exhibits excellent rheological behavior with good hydrophilicity.•HCS@CNT flow-electrode presents high average salt removal rate and prominent charge efficiency.•HCS@CNT demonstrates large potential for treating high concentration of salt solution.•DFT calculation reveals HCS@CNT is conducive to the interfacial charge transfer from HCS to CNT. Flow-electrode capacitive deionization (FCDI) emerges as a promising desalination technique, characterized by its unlimited desalination capacity, seamless operation, and easy scalability. However, challenges such as discontinuous electronic network, inadequate dispersion of suspended carbon particles, and hindered electron/ion transport pathways have impeded the full potential of FCDI. This study addresses the above issues by synergistically leveraging the advantage of hollow carbon sphere (HCS) and CNT to construct a flexible, continuous three-dimensional conductive network (HCS@CNT) as the flow-electrode for FCDI. The incorporation of HCS substantially improves the fluidity and effective collision of the flow-electrode slurry. Simultaneously, the bridging effect of CNT facilitates smooth ion transport routes and rapid electron/ion transfer. Moreover, the spherical structure of HCS as a node can effectively alleviate the agglomeration of CNT due to its inherent good fluidity. As a result, the meticulously designed HCS@CNT flow-electrode demonstrates outstanding rheological behavior with excellent hydrophilicity, a large specific capacitance, and low ion diffusion resistance. During desalination tests, the HCS@CNT flow-electrode exhibited a high average salt removal rate (0.56 µmol min−1 cm−2), appropriate energy-normalized removal salt (15 µmol J−1), and notable charge efficiency (89 %) in a 1 g L-1 NaCl solution. Impressively, it maintained good stability and continuity over a continuous 10-hour desalination process, showcasing substantial potential for treating highly concentrated saline water. In addition, density functional theory (DFT) calculations provided additional insights, confirming that the construction of HCS@CNT facilitated interfacial charge transfer and electron transport from HCS to CNT. This innovative approach sheds light on enhancing electron/ion transfer by harnessing the unique structural characteristics of the flow-electrode.